Aaron "Wheelz" Fotheringham not only flips a catastrophic negative into a positive, he double back flips it.

Confined to a wheelchair because of a spinal birth defect, the 19-year-old Las Vegan has ridden that wheelchair to extreme-sports stardom and a prominent slot in the first Nitro Circus Live tour.

"For me, confined isn't the right word," Fotheringham says, chuckling as he does between most of his thoughts. "I like being on a wheelchair."

Based on the MTV reality show "Nitro Circus," the tour kicks off its American leg on Saturday at the MGM Grand with a cavalcade of motocross and skate stars including Travis Pastrana, Jake Brown, Chad Kagy and Cam Sinclair.

"He's the most positive, genuinely happy guy you'd ever meet in your life," says Pastrana, the show's headliner and organizer, who reports that Fotheringham taunts him by busting out wheelchair tricks during everyday activities and then declaring: "Bet you wish you could have your motorcycle with you all the time!"

Fotheringham -- who attended Arbor View and Centennial high schools before earning his GED -- was launched onto his first quarter pipe at age 8 by his BMX-enthused older brother, Brian.

"He either wanted to see his little brother get hurt or do something cool," Fotheringham says. "Then I kept trying it until I landed it and I got hooked."

By 2006, Fotheringham became the first person to execute a back flip in a wheelchair. Last year, he was up to double back flips and he's currently thinking triple.

"I definitely think it's doable," he says, "if I have the right ramp and speed."

And yet he still encounters people who assume he can't be a real athlete.

"ER people don't really believe a kid in a wheelchair who comes in and is like, 'Hey, I just fell 20 feet out of the air onto my head,' " he says.

Fotheringham is phoning from Norco, Calif., where he's helping to fabricate a new chair for the tour with his partner in a yet-to-be-named new company. (Wheelchair design is where he wants to steer his career once this daredevil thing runs its course.)

"We're trying to get more people riding and jumping their wheelchairs," he says. "Over the years, I've been the guinea pig and we've learned where we need to strengthen and what we need to do."

Fotheringham has always made a special point of proving that he not only can do anything that anyone else can, but he can do it better. That's why, when he practices at Doc Romeo Pro Park, he won't use the handicap ramp to enter. Instead, he jumps up the stairs.

"Give me a challenge," he says. (Also, he points out, the stairs are faster.)

Fotheringham says he can't move his legs, but can feel them, "which is kind of weird."

"People think, 'Oh, well it doesn't hurt him when he falls,' " he says. "I'm like, uh, yeah it does!"

So far, his injuries have never surpassed a torn rotator cuff.

"Just some pops and clicks," he says.

To this day, Fotheringham claims he has never read up on spina bifada. He says he doesn't want to know what limitations his condition, an incomplete formation of the spine occurring in less than 1 of every 1,000 live U.S. births, is supposed to impose.

"I don't care," he says. "I've gotten all these great opportunities from it. I probably wouldn't be touring with Nitro Circus if I wasn't in a wheelchair."

Fotheringham plans to use the Las Vegas show -- which is being filmed for a 3-D movie slated for 2012 release -- to debut a dangerous new stunt.

"It's my hometown," he says. "I gotta do something cool. I don't want to do the same old tricks."

The plan is to lift himself entirely out of his comfort zone -- and the chair he's always strapped himself into.

"I want to be able to show that the wheelchair doesn't own me, and that I can actually leave the wheelchair in the air," he says, adding, with a chuckle: "It's gonna be sick."